The present invention relates to a radio telephone, preferably for use in cellular telecommunications, comprising an apparatus housing and at least one antenna, which is mounted on or in connection with the apparatus housing for performing the wireless communication of the radio telephone by transmitting and receiving radiofrequent electromagnetic waves within a certain wavelength range.
During the last decade the above-mentioned technical field has been the subject of a very rapid growth. As portable mobile telephones have become more compact and useful, they have gained popularity, and today mobile telephones are used by a major portion of the population in many countries.
A problem with the compact and low-weight mobile telephones of today is the signal degradation, which occurs during calls due to the mobile telephone antenna being located proximate to the user""s body, the hand and the head in particular. This interaction between the body and the near field of the antenna will normally cause deteriorated antenna properties, mainly because of reflections and absorption losses. The shorter the distance is between the antenna and the user, the larger becomes the signal degradation. This means that requirements for satisfactory antenna efficiency are difficult to fulfil together with requirements for physical compactness and robustness.
Modern mobile telephones often use quarterwave type antennas in addition to, or as replacement for, longer halfwave type antennas. Quarterwave antennas have the advantage of a compact and robust size, particularly if the antenna is realized as a helix antenna. A feature of quarterwave antennas is that they generate electric currents in and/or on the mobile telephone chassis. Since the chassis has conductive propertiesxe2x80x94for practical reasons the chassis is produced from metal or metallized plasticsxe2x80x94such chassis currents themselves generate electromagnetic fields, wherein the antenna efficiency is reduced because of the interaction with the user, as described above.
A high antenna efficiency is desired not only because the communication quality is improved, for instance as an increased signal-to-noise ratio, but also because this provides for a lower power consumption and consequently prolonged usage time as well as reduced heat generation. In order to improve the antenna efficiency it is previously known to maximize the distance between the antenna and the user""s head. One example is given in JP-A-7212822 and in EP-A-0 689 297, in which an antenna is arranged on top of a longside of the mobile telephone, while a speaker and a microphone are arranged at an opposite longside. Thus, the telephone is intended to be held in such a way, that the longside with the speaker and the microphone is in contact with the user""s head, while the opposite longside with the antenna will be relatively far from the user.
DE-A-43 00 705 discloses a portable telephone, wherein a conductive plate is arranged to act as a virtual ground plane for preventing high-frequency currents from being generated in the telephone body.
Furthermore, it is known to provide the mobile telephone with means for screening, absorbing or reflecting electromagnetic radiation. Such means may be arranged along the side of the antenna facing the user, and also on or inside the telephone chassis. Examples of previously known radio telephones of this kind are disclosed in U.S. Pat Nos. 5,493,704, 5,335,366, W095/31048 and JP-A-7123463.
A main object of the present invention is to provide a radio telephone with high antenna efficiency by reducing the electrical energy losses and minimizing the interaction between antenna and user, without limiting the opportunities to realize the radio telephone in a compact size and with an antenna well suited for communication.
A further object of certain embodiments of the invention is to provide a compact radio telephone with a large space for display and keypad.
The above-mentioned main object is achieved by a radio telephone, preferably for cellular telecommunication, comprising an apparatus housing and at least one antenna, which is mounted on or in connection with the apparatus housing for performing the wireless communication of the radio telephone by transmitting and receiving radio frequent electromagnetic waves in a certain wavelength range, wherein a current-reducing means is mounted to the apparatus housing between the antenna and the side of the radio telephone, which normally is in contact with a human user, the current-reducing means having conductive as well as dielectric properties and being arranged to reduce or eliminate electric currents present in and/or on the apparatus housing between the antenna and said side of the radio telephone.
Preferred embodiments of the invention are defined by the subsequent dependent claims.